Method for measuring specific surface area with dynamic surface area meter

Abstract

The present application relates to the field of physical adsorption apparatus, and particularly provides a method for measuring specific surface area by using a dynamic specific surface area apparatus, aiming at solving the problem of long testing time and low efficiency of the existing specific surface area testing method. To this end, the method comprises: after a sample to be tested is placed in the dynamic specific surface area apparatus, a first measurement curve of voltage change with time of the sample to be tested containing adsorption peak / desorption peak is obtained; based on the voltage on the adsorption peak / desorption peak on the first measurement curve, the corresponding adsorbed gas concentration on the standard curve is obtained; based on the obtained adsorbed gas concentration, the total adsorption amount / total desorption amount of the sample to be tested is determined; based on the total adsorption amount / total desorption amount, the specific surface area of the sample to be tested is determined; wherein the standard curve is a pre-stored curve of voltage change with adsorbed gas concentration. The above method has fast testing speed, does not require quantitative peaks, thereby saving the quantitative ring system, and saving the cost and internal space of the apparatus.

Description

Technical Field

[0001] This invention relates to the field of physical adsorption instruments, and specifically provides a method for measuring specific surface area using a dynamic specific surface area meter. Background Technology

[0002] Currently, the commonly used methods for determining specific surface area include static volumetric method and dynamic flow chromatography, among which dynamic flow chromatography is further divided into direct comparison method and single-point / multi-point method.

[0003] For dynamic surface area measurement methods, if the direct comparison method is used, the test results will be greatly affected by the peak shape of the standard sample and the sample to be tested. If the single-point / multi-point method is used, a quantitative loop is required, which requires an additional quantitative system, increasing costs. In addition, the quantitative loop needs to be calibrated frequently. Whether it is the direct comparison method or the single-point / multi-point BET method, a standard peak or quantitative peak needs to be obtained first when testing the sample, and then the sample peak is obtained, which makes the test time long and inefficient.

[0004] Accordingly, there is a need in the art for a new method for measuring specific surface area using a specific surface area meter to solve the above problems. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problems of long testing time and low efficiency of existing specific surface area testing methods.

[0006] In a first aspect, the present invention provides a method for measuring specific surface area using a dynamic surface area analyzer, characterized in that the method includes: after placing a sample to be tested in the dynamic surface area analyzer, acquiring a first measurement curve of the voltage of the sample to be tested, including adsorption peaks / desorption peaks, changing over time; obtaining the concentration of adsorbed gas corresponding to the adsorption peaks / desorption peaks on the first measurement curve; determining the total adsorption amount / total desorption amount of the sample to be tested based on the obtained adsorbed gas concentration; and determining the specific surface area of ​​the sample to be tested based on the total adsorption amount / total desorption amount; wherein the standard curve is a pre-stored curve of voltage changing with the concentration of adsorbed gas.

[0007] Using the above scheme, the step of measuring standard samples is eliminated when measuring the test sample, eliminating the need to wait for standard peaks or quantitative peaks. With four independent workstations, the testing efficiency can reach four samples in five minutes, resulting in fast testing speed. Furthermore, since this method does not require testing standard samples when testing the test sample, it avoids the influence of standard samples on the results. Moreover, since this method does not require quantitative peaks, it eliminates the need for a quantitative loop system, saving costs and instrument internal space. It also reduces nitrogen consumption, lowering costs.

[0008] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the method for obtaining the standard curve includes: retrieving a pre-stored original curve showing the change of voltage with the concentration of the adsorbed gas; executing a loop process until a preset condition is met; the loop process includes: shifting the original curve to obtain an offset curve; calculating the first theoretical specific surface area of ​​the standard sample based on the offset curve; comparing the first theoretical specific surface area with the known specific surface area of ​​the standard sample; wherein, the preset condition is that the first theoretical specific surface area is equal to the known specific surface area; after exiting the loop process, the offset curve corresponding to the first theoretical specific surface area equal to the known specific surface area is used as the standard curve.

[0009] Using the above scheme, since the original curve was found to be a straight line, the method of curve correction using standard samples and offset curves not only improves the accuracy of calibration but also increases the calibration rate. This correction method makes testing with the corrected standard curve more accurate, and since a quantitative loop is not required, there is no need to worry about errors caused by changes in the volume of the quantitative loop.

[0010] In a preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic surface area analyzer, the method further includes: after placing the standard sample in the dynamic surface area analyzer, acquiring a second measurement curve of the voltage of the standard sample, including the adsorption peak / desorption peak, changing over time; the step of "calculating the first theoretical specific surface area of ​​the standard sample based on the offset curve" further includes: obtaining the concentration of adsorbed gas corresponding to the offset curve based on the voltage of the adsorption peak / desorption peak on the second measurement curve; determining the total adsorption amount / total desorption amount of the standard sample based on the obtained adsorbed gas concentration; and determining the first theoretical specific surface area of ​​the standard sample based on the total adsorption amount / total desorption amount.

[0011] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the structure used to obtain the original curve includes a thermal conductivity cell. The inlet of the reference arm and the inlet of the measuring arm of the thermal conductivity cell are both used to receive a mixture of adsorbed gas and carrier gas. The outlet of the reference arm and the outlet of the measuring arm of the thermal conductivity cell are both connected to the outside air. The method for obtaining the original curve includes: introducing a mixture of gas with a preset adsorbed gas concentration into both the inlet of the reference arm and the inlet of the measuring arm; changing the concentration of adsorbed gas introduced into the inlet of the measuring arm; collecting the voltage corresponding to different adsorbed gas concentrations in the measuring arm to obtain a curve showing the change of voltage with the adsorbed gas concentration, and recording this curve as the original curve.

[0012] By adopting the above scheme, the original curve can be made as close as possible to the actual standard curve, thereby improving the calibration rate of the original curve and the accuracy of the obtained standard curve.

[0013] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the step of "shifting the original curve to obtain an offset curve" further includes: selecting a point on the original curve at a preset concentration of adsorbed gas as the origin; shifting the original curve around the origin to obtain an offset curve.

[0014] Using the above scheme, the offset curve can be made very close to the standard curve, thus enabling the standard curve to be obtained more quickly, reducing the number of calculation steps, and further improving the calibration rate.

[0015] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the number of standard curves is multiple, and each standard curve corresponds to a known specific surface area and a known area to be measured for a different standard sample; the step of "obtaining the adsorbed gas concentration corresponding to the standard curve based on the voltage of the adsorption peak / desorption peak on the first measurement curve" further includes: obtaining the adsorbed gas concentration corresponding to each standard curve based on the voltage of the adsorption peak / desorption peak on the first measurement curve; the step of "determining the total adsorption amount / total desorption amount of the sample to be tested based on the obtained adsorbed gas concentration" further includes: determining the total adsorption amount / total desorption amount of the sample to be tested based on the adsorbed gas concentration corresponding to each standard curve. The step of "determining the specific surface area of ​​the test sample based on the total adsorption / total desorption of each standard curve" further includes: determining the second theoretical specific surface area corresponding to each standard curve based on the total adsorption / total desorption of the test sample corresponding to each standard curve; determining the theoretical test area of ​​the standard sample corresponding to each standard curve based on the second theoretical specific surface area corresponding to each standard curve; comparing the error between the second theoretical specific surface area of ​​each standard curve and the known specific surface area, and comparing the error between the theoretical test area and the known test area; determining the standard curve closest to the test sample based on the comparison results; and determining the specific surface area of ​​the test sample based on the closest standard curve.

[0016] Since the standard curve obtained by calibrating with only one standard sample cannot be perfectly applied to all test samples with different surface areas, this invention uses multiple standard samples with different test areas to create multiple standard curves during calibration. When testing the test sample, the software selects the curve that is closest to the test sample based on the test area and surface area of ​​the test sample for calculation, making the results more accurate.

[0017] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the step of "comparing the error between the second theoretical specific surface area of ​​each standard curve and the known specific surface area, and the error between the theoretical area to be measured and the known area to be measured" further includes: comparing the relative error between the second theoretical specific surface area corresponding to each standard curve and the known specific surface area, and the sum of the relative errors between the corresponding theoretical area to be measured and the known area to be measured; the step of "determining the standard curve closest to the sample to be measured based on the comparison results" further includes: determining the standard curve with the smallest sum of relative errors as the standard curve closest to the sample to be measured; the step of "determining the specific surface area of ​​the sample to be measured based on the closest standard curve" further includes: determining the second theoretical specific surface area corresponding to the closest standard curve as the specific surface area of ​​the sample to be measured.

[0018] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the step of "obtaining the concentration of adsorbed gas on the standard curve based on the voltage at the adsorption peak / desorption peak on the first measurement curve" further includes: obtaining the concentration of adsorbed gas at each point on the standard curve based on the voltage at each point on the adsorption peak / desorption peak on the first measurement curve; the step of "determining the total adsorption amount / total desorption amount of the sample to be tested based on the obtained adsorbed gas concentration" further includes: determining the flow rate of adsorbed gas at each point based on the obtained adsorbed gas concentration at each point; determining the consumption amount of adsorbed gas at each point based on the flow rate of adsorbed gas at each point; and integrating the consumption amounts of all adsorbed gases to obtain the total adsorption amount / total desorption amount of the sample to be tested.

[0019] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area analyzer, the structure used to obtain the original curve further includes a first adsorbed gas tube, a first carrier gas tube, a first gas mixing device, a second adsorbed gas tube, a second carrier gas tube, and a second gas mixing device. The outlet of the first adsorbed gas tube and the outlet of the first carrier gas tube are respectively connected to the first inlet and the second inlet of the first gas mixing device, and the outlet of the first gas mixing device is connected to the inlet of the reference arm. The outlet of the second adsorbed gas tube and the outlet of the second carrier gas tube are respectively connected to the first inlet and the second inlet of the second gas mixing device, and the outlet of the second gas mixing device is connected to the inlet of the measuring arm. A mass flow controller is provided on each of the first adsorbed gas tube, the first carrier gas tube, the second adsorbed gas tube, and the second carrier gas tube.

[0020] In the preferred embodiment of the above-mentioned method for measuring specific surface area using a dynamic specific surface area meter, both the first gas mixing device and the second gas mixing device are gas mixing tanks. Attached Figure Description

[0021] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0022] Figure 1 This is a schematic diagram of the structure of the dynamic surface area analyzer of the present invention;

[0023] Figure 2 This is a diagram showing the main steps of the method for testing specific surface area using the dynamic specific surface area analyzer of the present invention;

[0024] Figure 3 This is a schematic diagram of the voltage change over time, including adsorption or desorption peaks, when the dynamic surface area analyzer of the present invention is used to test the specific surface area of ​​a sample.

[0025] Figure 4 This is a schematic diagram of the original curve of voltage change with nitrogen concentration according to the present invention;

[0026] Figure 5 This is a schematic diagram of the structure for obtaining the original curve according to the present invention;

[0027] Figure 6 This is a diagram showing the main steps of the method for obtaining the original curve according to the present invention;

[0028] Figure 7 This is a possible logic diagram of the method for obtaining the standard curve according to the present invention;

[0029] Figure 8 This is a schematic diagram illustrating the offsetting of the original curve according to the present invention.

[0030] List of reference numerals in the attached diagram:

[0031] 10-Thermal conductivity cell; 11-Reference arm; 12-Measuring arm; 20-First gas tube; 21-Second gas tube; 30-Gas mixing device; 40-Sample tube; 50-Mass flow controller; 60-First adsorbed gas tube; 61-First carrier gas tube; 62-First gas mixing device; 70-Second adsorbed gas tube; 71-Second carrier gas tube; 72-Second gas mixing device. Detailed Implementation

[0032] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art can make adjustments as needed to adapt to specific applications.

[0033] It should be noted that in the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, it should be noted that in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] To address the problems of long testing times and low efficiency in existing specific surface area testing methods, such as... Figure 1 As shown, the present invention provides a dynamic surface area analyzer. It can be understood that the dynamic surface area analyzer may include a thermal conductivity cell 10, a first air pipe 20, a second air pipe 21, and a gas mixing device 30. The outlet of the first air pipe 20 is connected to the first air inlet of the gas mixing device 30, the outlet of the second air pipe 21 is connected to the second air inlet of the gas mixing device 30, the outlet of the gas mixing device 30 is connected to the inlet of the reference arm 11 of the thermal conductivity cell 10, and a sample tube 40 is connected between the outlet of the reference arm 11 and the inlet of the measuring arm 12 of the thermal conductivity cell 10. A sample can be placed in the sample tube 40. The outlet of the measuring arm 12 is connected to the outside air so that the mixed gas sequentially passes through the reference arm 11 and the sample tube 40 to the measuring arm 12, and then exits from the outlet of the measuring arm 12. The first air pipe 20 and the second air pipe 21 may both be equipped with a mass flow controller 50 (i.e., MFC). It should be noted that the first gas tube 20 is used to receive the adsorbed gas, and the second gas tube 21 is used to receive the carrier gas, such as nitrogen gas and helium gas. Of course, the carrier gas can also be hydrogen gas, etc. For ease of explanation, the adsorbed gas of the present invention will be nitrogen gas and the carrier gas will be helium gas as an example in the following description.

[0035] Working principle: By controlling the mass flow controller 50 on the first gas pipe 20 and the second gas pipe 21, nitrogen and helium are passed through the reference arm 11 and the measuring arm 12 of the thermal conductivity cell 10 in a certain ratio. A sample tube 40 containing a test sample is connected between the reference arm 11 and the measuring arm 12. When the sample tube 40 is immersed in liquid nitrogen, the sample undergoes adsorption, and the gas concentration in the reference arm 11 and the measuring arm 12 of the thermal conductivity cell 10 becomes unbalanced. The thermal conductivity cell 10 outputs a voltage signal, which is acquired by a bridge circuit, amplified by an amplifier, converted by an AD converter using a data acquisition card, and input into a computer through a communication interface. The data is then analyzed and automatically saved by professional analysis software.

[0036] In this process, the sample adsorbs nitrogen gas at liquid nitrogen temperature, resulting in an adsorption peak; then, at room temperature or upon heating, it desorbs, producing a desorption peak. Therefore, a curve showing the voltage change over time for the sample containing either the adsorption or desorption peaks can be obtained.

[0037] like Figure 2 As shown, the method for measuring specific surface area using the dynamic specific surface area analyzer of the present invention includes:

[0038] Step S101: After the sample to be tested is placed in the dynamic surface area analyzer, acquire the first measurement curve of the voltage change over time for the sample, including the adsorption / desorption peaks. For example... Figure 3 As shown, this curve is the voltage change over time, including the adsorption / desorption peaks (horizontal axis: time, total axis: voltage).

[0039] Step S102: Based on the voltage at the adsorption / desorption peaks on the first measurement curve, obtain the nitrogen concentration (N2 / (N2+He)) corresponding to the standard curve. Wherein, as... Figure 4 As shown, the standard curve is a pre-stored curve of voltage changing with nitrogen concentration (the horizontal axis is voltage, and the vertical axis is nitrogen concentration).

[0040] It is possible to obtain the nitrogen concentration at each point on the standard curve based on the voltage at each point on the adsorption peak of the first measurement curve. Since each point on the adsorption peak of the sample is a voltage signal, the nitrogen concentration at each point can be converted using the voltage-nitrogen concentration standard curve. Specifically, a voltage value can be obtained by subtracting the corresponding baseline voltage from the voltage at each point on the adsorption peak, and then the nitrogen concentration corresponding to this voltage value can be obtained through the standard curve. Here, the baseline voltage is the voltage on the line connecting the adsorption start and end points. Similarly, the nitrogen concentration at each point on the standard curve can also be obtained from the voltage at each point on the desorption peak.

[0041] Step S103: Determine the total adsorption / desorption of the sample based on the obtained nitrogen concentration.

[0042] Taking adsorption as an example, one possible method for determining the total adsorption amount of the sample to be tested is to determine the nitrogen flow rate at each point based on the nitrogen concentration at each point; determine the nitrogen consumption at each point based on the nitrogen flow rate at each point; and integrate all the nitrogen consumption amounts to obtain the total adsorption amount of the sample to be tested.

[0043] Since nitrogen flow rate / helium flow rate = nitrogen concentration / helium concentration, i.e., nitrogen flow rate = (nitrogen concentration / helium concentration) * helium flow rate, and helium concentration = 1 - nitrogen concentration, therefore nitrogen flow rate = (nitrogen concentration / (1 - nitrogen concentration)) * helium flow rate. Because helium is not adsorbed during the experiment, the helium flow rate is always the total flow rate * (1 - nitrogen concentration at the adsorption initiation point). Since the total flow rate is known (obtained from the mass flow controller), the nitrogen flow rate at each point can be calculated. Then, by integrating over each point, the total amount of nitrogen adsorbed can be obtained. The nitrogen concentration at the adsorption initiation point is the nitrogen concentration at the peak of the adsorption.

[0044] The calculation principle for determining the total desorption amount of the sample based on the obtained nitrogen concentration is the same, and will not be elaborated further.

[0045] It should be noted that the above calculation method is one possible implementation. As long as the total adsorption / desorption of the sample to be tested can be determined based on the obtained nitrogen concentration, those skilled in the art can adjust the specific calculation method. For example, the nitrogen concentration of the corresponding points on the standard curve can be obtained based on the voltage of some points on the adsorption peak of the first measurement curve, the nitrogen consumption of some points can be obtained based on the nitrogen concentration of these points, a curve equation can be obtained based on the nitrogen consumption of these points, and then the curve equation can be integrated to obtain the total consumption of the sample to be tested, etc. All of these do not deviate from the principle of the present invention and are within the protection scope of the present invention.

[0046] Step S104: Determine the specific surface area of ​​the sample to be tested based on the total adsorption / total desorption.

[0047] In other words, after obtaining the total adsorption / total desorption ratio, the specific surface area of ​​the sample can be obtained using the BET equation. The method for determining the specific surface area of ​​a sample based on the total adsorption / total desorption ratio is already well-established and will not be elaborated upon here.

[0048] This invention directly retrieves a pre-stored standard curve for calculation, directly converting the voltage signal of the sample peak into nitrogen adsorption / desorption capacity, and then calculating the specific surface area of ​​the sample using the BET equation. This eliminates the need to measure standard samples when measuring the sample, eliminating the need to wait for standard or quantitative peaks. With four independent workstations, the testing efficiency can reach four samples in five minutes, resulting in fast testing speed. Furthermore, since this method does not require standard sample testing, it avoids the influence of standard samples on the results. Moreover, because this method does not require quantitative peaks, it eliminates the need for a quantitative loop system, saving costs and instrument space. It also reduces nitrogen consumption, lowering costs.

[0049] One possible method to obtain the standard curve is to retrieve a pre-stored original curve showing the change of voltage with nitrogen concentration, and then correct the original curve to obtain the standard curve.

[0050] like Figure 5 As shown, the structure for obtaining the original curve includes a thermal conductivity cell 10, a first adsorbed gas tube 60, a first carrier gas tube 61, a first gas mixing device 62, a second adsorbed gas tube 70, a second carrier gas tube 71, and a second gas mixing device 72. The outlet of the first adsorbed gas tube 60 and the outlet of the first carrier gas tube 61 are connected to the first inlet and the second inlet of the first gas mixing device 62, respectively. The outlet of the first gas mixing device 62 is connected to the inlet of the reference arm 11. The outlet of the second adsorbed gas tube 70 and the outlet of the second carrier gas tube 71 are connected to the first inlet and the second inlet of the second gas mixing device 72, respectively. The outlet of the second gas mixing device 72 is connected to the inlet of the measuring arm 12. The outlets of the reference arm 11 and the measuring arm 12 of the thermal conductivity cell 10 are both open to the outside air. Mass flow controllers 50 are installed on the first adsorbed gas tube 60, the first carrier gas tube 61, the second adsorbed gas tube 70, and the second carrier gas tube 71. The first gas mixing device 62 and the second gas mixing device 72 can take various forms. Preferably, both the first gas mixing device 62 and the second gas mixing device 72 are gas mixing tanks, which allows sufficient time for gas mixing, ensuring uniform gas mixing and reducing experimental errors. Of course, as long as the gas can be mixed, the specific forms of the first gas mixing device 62 and the second gas mixing device 72 can be adjusted, for example, they can be replaced with a three-way valve.

[0051] The thermal conductivity cell 10 for acquiring the original curve can be the same thermal conductivity cell 10 as the thermal conductivity cell 10 of the dynamic surface area analyzer. The first adsorbed gas tube 60 can be the first gas tube 20 of the dynamic surface area analyzer, the first carrier gas tube 61 can be the second gas tube 21 of the dynamic surface area analyzer, and the first gas mixing device 62 can be the gas mixing device of the dynamic surface area analyzer. When performing specific surface area measurement, the second gas mixing device 72, the second adsorbed gas tube 70, and the second carrier gas tube 71 on one side of the measuring arm 12 of the structure for acquiring the original curve can be removed, so that the outlet of the reference arm 11 is connected to the inlet of the measuring arm 12, and the sample tube 40 is connected between the two, and the sample tube 40 is immersed in the liquid nitrogen cup.

[0052] The mass flow controller 50 is used to adjust and control the flow rates of nitrogen and helium. It can be understood that the first adsorbed gas tube 60 and the second adsorbed gas tube 70 are used to receive nitrogen, and the first carrier gas tube 61 and the second carrier gas tube 71 are used to receive helium.

[0053] like Figure 6 As shown, the method for obtaining the original curve of the thermal conductivity cell according to the present invention will be described below. Specifically, it includes the following steps.

[0054] Step S201: Introduce a mixture of gases with a preset nitrogen concentration into both the inlet of the reference arm and the inlet of the measuring arm.

[0055] That is, nitrogen and helium are introduced into the first adsorbed gas tube and the first carrier gas tube, respectively. After passing through the first mixing device, the nitrogen and helium are mixed evenly to form a nitrogen-helium mixture. The mixture is then introduced into the thermal conductivity cell through the inlet of the reference arm. The nitrogen concentration in the reference arm is maintained at a preset nitrogen concentration, for example, 30%, by adjusting the mass flow controllers on the first adsorbed gas tube and the first carrier gas tube, respectively, using software. Similarly, the nitrogen concentration in the measuring arm is maintained at the same preset nitrogen concentration by controlling the mass flow controllers on the second adsorbed gas tube and the second carrier gas tube.

[0056] Step S202: Change the nitrogen concentration introduced into the inlet of the measuring arm.

[0057] By controlling the mass flow controllers on the second adsorbed gas tube and the second carrier gas tube, the nitrogen concentration introduced into the measuring arm can be changed, thereby obtaining mixed gases with different nitrogen-helium ratios. For example, the nitrogen concentration in the measuring arm can be adjusted to 0.02, 0.04, 0.06...0.3.

[0058] Step S203: Collect the voltage corresponding to different nitrogen concentrations on the measuring arm to obtain a curve of voltage changing with nitrogen concentration, and record this curve as the original curve.

[0059] For example, when the nitrogen concentration in the measuring arm is 0.02, 0.04, 0.06…0.3, a curve of the thermal conductivity cell voltage signal corresponding to p / p0 (nitrogen concentration) from 0 to 0.3 is obtained. This curve of voltage change with nitrogen concentration is recorded as the original curve and stored. It can be understood that a voltage signal will be generated whenever the nitrogen concentration in the measuring arm is different from that in the reference arm; if the nitrogen concentrations in the reference arm and the measuring arm are the same, the output voltage signal will be 0.

[0060] Due to the differences between each thermal conductivity cell, the original curves of the thermal conductivity cells will be slightly different. In order to ensure the accuracy of the measurement, it is necessary to correct the original curves again to obtain the standard curves corresponding to each thermal conductivity cell as described above.

[0061] like Figure 7 As shown, the method for obtaining the standard curve of the present invention by modifying the original curve may include the following steps.

[0062] Step S301: After the standard sample is placed in the dynamic surface area analyzer, a second measurement curve showing the voltage change of the standard sample over time, including the adsorption / desorption peaks, is obtained.

[0063] First, a standard sample is placed in the sample tube of the dynamic surface area analyzer, allowing for the acquisition of a second measurement curve showing the voltage change over time, including adsorption / desorption peaks. It is understood that the standard sample has a known specific surface area, a known area to be measured, and a known mass.

[0064] Step S302: Retrieve the pre-stored original curve of voltage changing with nitrogen concentration.

[0065] Step S303: Offset the original curve to obtain the offset curve.

[0066] like Figure 8 As shown, studies of multiple thermal conductivity cells revealed that the original nitrogen concentration-voltage (p / p0-mV) curve for each cell was almost a straight line, representing a binomial equation, i.e., ax 2 Therefore, curve calibration can be performed by offsetting the original curve.

[0067] In a preferred embodiment, a point on the original curve at a preset nitrogen concentration is selected as the origin, and the original curve is offset around the origin to obtain an offset curve. For example, in steps S201-S203, the point with a nitrogen concentration of 0.3 is selected as the origin, and the TCD voltage signal corresponding to the point p / p0 = 0.3 can be set to 0mV, as shown in the figure. The curves of different thermal conductivity cells are actually the original curve offset to the left or right with 0.3 as the origin, resulting in a new curve.

[0068] Of course, the above-described offset method is a preferred embodiment. Those skilled in the art can adjust the offset method of the original curve, such as offsetting the entire curve above or below the Y-axis.

[0069] Step S304: Calculate the first theoretical specific surface area of ​​the standard sample based on the offset curve.

[0070] Based on the voltage at the adsorption / desorption peaks on the second measurement curve, the nitrogen concentration corresponding to the offset curve is obtained; based on the obtained nitrogen concentration, the total adsorption / desorption amount of the standard sample is determined; based on the total adsorption / desorption amount, the first theoretical specific surface area of ​​the standard sample is determined. Detailed methods for obtaining the first theoretical specific surface area are described in steps S102 to S104, and will not be repeated here.

[0071] Step S305: Compare the first theoretical specific surface area with the known specific surface area of ​​the standard sample.

[0072] Step S306: Determine whether the first theoretical specific surface area is equal to the known specific surface area of ​​the standard sample. If not, continue with steps S303 to S305, that is, continue to shift the original curve and calculate the first theoretical specific surface area based on the shifted curve. Until the first theoretical specific surface area is equal to the known specific surface area of ​​the standard sample, proceed to step S307: Use the shifted curve corresponding to the first theoretical specific surface area that is equal to the known specific surface area as the standard curve. This means that the first theoretical specific surface area can be calculated from the shifted curve.

[0073] The above correction method makes the test using the corrected standard curve more accurate. Since there is no need to use a quantitative loop, there is no need to worry about errors caused by changes in the volume of the quantitative loop.

[0074] In one possible implementation, there are multiple standard curves, each corresponding to a different known specific surface area and a known area to be measured for a standard sample. Different sizes of standard samples can be used to correspond to different standard curves using the method described above. In other words, this invention pre-stores multiple standard curves, and each standard curve corresponds to a known specific surface area and a known area to be measured for a standard sample. In this case, the method for measuring specific surface area using a dynamic surface area analyzer is as follows:

[0075] Based on the voltage at the adsorption / desorption peaks on the first measurement curve, the nitrogen concentration corresponding to each standard curve is obtained. Based on the nitrogen concentration corresponding to each standard curve, the total adsorption / desorption amount of the test sample corresponding to each standard curve is determined. Based on the total adsorption / desorption amount of the test sample corresponding to each standard curve, the second theoretical specific surface area corresponding to each standard curve is determined. That is, after completing step S101, the second theoretical specific surface area of ​​the standard sample corresponding to each standard curve is calculated using the specific surface area measurement method in steps S102 to S104. The specific calculation method has been explained in the above steps and will not be repeated here.

[0076] After obtaining the second theoretical specific surface area corresponding to each standard curve, the theoretical test area of ​​the standard sample corresponding to each standard curve is determined based on the second theoretical specific surface area. This can be obtained by multiplying the second theoretical specific surface area by the mass of the corresponding standard sample, or by multiplying the second theoretical specific surface area by the density and volume of the corresponding standard sample. Then, the error between the second theoretical specific surface area of ​​each standard curve and the known specific surface area, as well as the error between the theoretical test area and the known test area, are compared. Based on the comparison results, the standard curve closest to the test sample is determined, and the specific surface area of ​​the test sample is determined based on the closest standard curve.

[0077] Specifically, the relative error between the second theoretical specific surface area corresponding to each standard curve and the known specific surface area, as well as the sum of the relative errors between the corresponding theoretical test area and the known test area, can be compared. The standard curve with the smallest sum of relative errors is determined as the standard curve closest to the test sample, and the second theoretical specific surface area corresponding to the closest standard curve is determined as the specific surface area of ​​the test sample.

[0078] Possibly, the formula for calculating the relative error in this invention is δ = (X - X1) divided by X. For example, if the known specific surface area of ​​standard curve A is a, and the first theoretical specific surface area is a1, the relative error δ1 between the two is |a - a1| divided by a. If the theoretical area to be measured is b, and the known area to be measured is b1, the relative error δ1 between the two is |b - b1| divided by b. The sum of δ1 and δ2 is the sum of the relative errors. The sum of the relative errors of standard curves B, ..., etc., is calculated using the same method, and the standard curve with the smallest sum of relative errors is selected as the standard curve closest to the sample to be tested.

[0079] Of course, the calculation method described above is a preferred embodiment. Other calculation methods can also be used in this invention. For example, comparing the absolute error between the second theoretical specific surface area and the known specific surface area corresponding to each standard curve, and the sum of the absolute errors between the corresponding theoretical test area and the known test area, to determine the standard curve with the smallest sum of absolute errors as the standard curve closest to the test sample, etc. These methods do not deviate from the principles of this invention and are all within the scope of protection of this invention.

[0080] Since the standard curve obtained by calibrating with only one standard sample cannot be perfectly applied to all test samples with different surface areas, this invention uses multiple standard samples with different test areas to create multiple standard curves during calibration. When testing the test sample, the software selects the curve that is closest to the test sample based on the test area and surface area of ​​the test sample for calculation, making the results more accurate.

[0081] Those skilled in the art will understand that although the steps in the above embodiments are described in the above order, they will understand that in order to achieve the effect of this embodiment, different steps do not necessarily need to be executed in this order. They can be executed simultaneously (in parallel) or in a reverse order. For example, step S301 can be executed after or simultaneously with step S302 or step S303. These simple variations are all within the protection scope of this invention.

[0082] It should be noted that the above embodiments are merely used to illustrate the principles of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the principles of the present invention, those skilled in the art can adjust the above methods and structures so that the present invention can be applied to more specific application scenarios.

[0083] For example, although this invention is described as obtaining a standard curve by calibrating the original curve, this is not intended to limit the scope of protection of this invention. For example, if the standard curve is obtained by empirical formula, etc., these do not deviate from the principle of this invention and are all within the scope of protection of this invention.

[0084] For example, the method for obtaining the original curve of the present invention is not unique. For example, it can be obtained by empirical formulas, etc., and these methods do not deviate from the principle of the present invention and are all within the protection scope of the present invention.

[0085] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for measuring specific surface area with a dynamic surface area analyzer, characterized by, The method comprises: After the sample to be measured is placed in the dynamic specific surface area meter, a first measurement curve of voltage change over time of the sample to be measured containing adsorption peak / desorption peak is obtained; Based on the voltage on the adsorption peak / desorption peak on the first measurement curve, the corresponding adsorbed gas concentration on the standard curve is obtained; Based on the obtained adsorbed gas concentration, the total adsorption amount / desorption amount of the sample to be measured is determined; Based on the total adsorption amount / desorption amount, the specific surface area of the sample to be measured is determined; The standard curve is a pre-stored curve of voltage change over adsorbed gas concentration; The method for obtaining the standard curve comprises: Retrieve the pre-stored original curve of voltage change over adsorbed gas concentration; Perform a loop process until a preset condition is met; the loop process comprises: Shift the original curve to obtain a shifted curve; Calculate the first theoretical specific surface area of the standard sample based on the shifted curve; Compare the size of the first theoretical specific surface area with the known specific surface area of the standard sample; The preset condition is that the first theoretical specific surface area is equal to the known specific surface area; After exiting the loop process, the shifted curve corresponding to the first theoretical specific surface area equal to the known specific surface area is taken as the standard curve.

2. The method of measuring the specific surface area with the dynamic surface area analyzer according to claim 1, characterized by, The method further comprises: After the standard sample is placed in the dynamic specific surface area meter, a second measurement curve of voltage change over time of the standard sample containing adsorption peak / desorption peak is obtained; The step of "calculating the first theoretical specific surface area of the standard sample based on the shifted curve" further comprises: Based on the voltage on the adsorption peak / desorption peak on the second measurement curve, the corresponding adsorbed gas concentration on the shifted curve is obtained; Based on the obtained adsorbed gas concentration, the total adsorption amount / desorption amount of the standard sample is determined; Based on the total adsorption amount / desorption amount, the first theoretical specific surface area of the standard sample is determined.

3. The method for measuring the specific surface area of the dynamic specific surface area meter according to claim 1, wherein The structure for obtaining the original curve comprises a thermal conductivity cell, the inlet of the reference arm and the inlet of the measuring arm of the thermal conductivity cell are used to receive mixed gas of adsorbed gas and carrier gas, the outlet of the reference arm and the outlet of the measuring arm of the thermal conductivity cell are in communication with the outside air; The method for obtaining the original curve comprises: The inlet of the reference arm and the inlet of the measuring arm are both connected to the mixed gas with a preset adsorbed gas concentration; Change the adsorbed gas concentration of the inlet of the measuring arm; Collect the voltage corresponding to different adsorbed gas concentrations of the measuring arm to obtain a curve of voltage change over adsorbed gas concentration, and mark this curve as the original curve.

4. The method for measuring the specific surface area of the dynamic specific surface area meter according to claim 2, wherein The step of "shifting the original curve to obtain a shifted curve" further comprises: Select a point at a preset adsorbed gas concentration on the original curve as an origin; Shift the original curve around the origin to obtain a shifted curve.

5. The method of measuring specific surface area by using the dynamic specific surface area apparatus according to claim 1, wherein, the number of the standard curves is plural, and each of the standard curves corresponds to a known specific surface area and a known measured area of a standard sample; the step of "obtaining the corresponding adsorbed gas concentration on the standard curve based on the voltage on the adsorption peak / desorption peak on the first measurement curve" further comprises: obtaining the corresponding adsorbed gas concentration on each of the standard curves based on the voltage on the adsorption peak / desorption peak on the first measurement curve; the step of "determining the total adsorption amount / desorption amount of the measured sample based on the obtained adsorbed gas concentration" further comprises: determining the total adsorption amount / desorption amount of the measured sample corresponding to each of the standard curves based on the corresponding adsorbed gas concentration on each of the standard curves; the step of "determining the specific surface area of the measured sample based on the total adsorption amount / desorption amount" further comprises: determining the second theoretical specific surface area corresponding to each of the standard curves based on the total adsorption amount / desorption amount of the measured sample corresponding to each of the standard curves; determining the theoretical measured area of the standard sample corresponding to each of the standard curves based on the second theoretical specific surface area corresponding to each of the standard curves; comparing the error size of the second theoretical specific surface area with the known specific surface area and the error size of the theoretical measured area with the known measured area of each standard curve; determining the standard curve closest to the measured sample based on the comparison result; and determining the specific surface area of the measured sample based on the closest standard curve.

6. The method of measuring specific surface area by using the dynamic specific surface area apparatus according to claim 5, wherein, the step of "comparing the error size of the second theoretical specific surface area with the known specific surface area and the error size of the theoretical measured area with the known measured area of each standard curve" further comprises: comparing the sum of the relative error of the second theoretical specific surface area with the known specific surface area and the relative error of the corresponding theoretical measured area with the known measured area corresponding to each standard curve; the step of "determining the standard curve closest to the measured sample based on the comparison result" further comprises: determining the standard curve with the smallest sum of the relative errors as the standard curve closest to the measured sample; and the step of "determining the specific surface area of the measured sample based on the closest standard curve" further comprises: determining the second theoretical specific surface area corresponding to the closest standard curve as the specific surface area of the measured sample.

7. The method of measuring specific surface area by using the dynamic specific surface area apparatus according to claim 1, wherein, the step of "obtaining the corresponding adsorbed gas concentration on the standard curve based on the voltage on the adsorption peak / desorption peak on the first measurement curve" further comprises: obtaining the corresponding adsorbed gas concentration of each point on the standard curve based on the voltage of each point on the adsorption peak / desorption peak on the first measurement curve. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The step of "determining the total adsorption amount / desorption amount of the sample to be measured based on the obtained adsorbed gas concentration" further comprises: determining the flow rate of the adsorbed gas at each point based on the obtained adsorbed gas concentration at each point; determining the consumption amount of the adsorbed gas at each point based on the flow rate of the adsorbed gas at each point; integrating all the consumption amounts of the adsorbed gas to obtain the total adsorption amount / desorption amount of the sample to be measured.

8. The method for measuring specific surface area by using the dynamic specific surface area meter according to claim 3, wherein, the structure for obtaining the original curve further comprises a first adsorbed gas pipe, a first carrier gas pipe, a first gas mixing device, a second adsorbed gas pipe, a second carrier gas pipe, and a second gas mixing device, the gas outlet of the first adsorbed gas pipe and the gas outlet of the first carrier gas pipe are respectively connected to the first gas inlet and the second gas inlet of the first gas mixing device, and the gas outlet of the first gas mixing device is connected to the inlet of the reference arm; the gas outlet of the second adsorbed gas pipe and the gas outlet of the second carrier gas pipe are respectively connected to the first gas inlet and the second gas inlet of the second gas mixing device, and the gas outlet of the second gas mixing device is connected to the inlet of the measuring arm; the first adsorbed gas pipe, the first carrier gas pipe, the second adsorbed gas pipe, and the second carrier gas pipe are all provided with mass flow controllers.

9. The method for measuring specific surface area by using the dynamic specific surface area meter according to claim 8, wherein, the first gas mixing device and the second gas mixing device are both gas mixing tanks.

Images